A lane departure warning apparatus (LDW: Lane Departure Warning) which outputs a warning when the departure from the traveling lane is predicted, and a lane keeping assist apparatus (LKA: Lane Keeping Assist) which adds a steering force for traveling at a center of the traveling lane are known. In these apparatuses, white lines are recognized using a camera and an image processor installed in a vehicle.
In the LDW/LKA, it is general practice to notify a driver of a current operation status of the LDW/LKA (see Patent Document 1, for example). This is because there is a case in which the output of the warning or the lane keeping assistance is not performed, depending on a white line recognition status, for example, even if a switch of the LDW/LKA is turned on. Patent Document 1 discloses a white line display apparatus for a vehicle for displaying a white line icon on the display device in which the white line icon is displayed in a solid white if the white line is recognized by white line recognition means and the white line icon is displayed in outline if the white line is not recognized by white line recognition means.
FIG. 1A illustrates an example of a display status of the white line if the white line is recognized in the LDW/LKA, and an example of a display status of the white line if the white line is not recognized in the LDW/LKA. The recognition status of the white line is displayed as the white line icon on the display device such as a liquid crystal display. For example, the white line icon is displayed in a bold manner if the white line is recognized and white line icon is displayed in a slender manner so that a driver can understand that the white line is not recognized. If the white line is not recognized, the LDW/LKA cannot predict the departure from the traveling lane to output the warning and add the steering force for traveling at the center of the lane.
The reasons why the white line is not recognized include cases where a road surface sign does not exist, the white line is patchy or unclear due to hard rainfall, a wiper device operates in a high speed mode, the driver performs a predetermined operation such as a lane change, etc.
As illustrated in FIG. 1A, by notifying the driver of the fact that the LDW/LKA does not operate, it is possible to prevent the driver from overtrusting the LDW/LKA. In other words, it is possible to prevent the driver from expecting an excessive performance of the LDW/LKA, thereby notifying the driver that there is a limit of the assistance in a status where the white line is not recognized. Further, it is possible to notify the driver of the fact that there may be a case where the LDW/LKA does not operate normally when a view field of a camera is shielded due to an undesirable position of an inspection sticker or an antenna for ETC (Electronic Toll Collection).
There are some vehicles in which the LDW/LKA can perform the lane departure warning or the lane keeping assist even if the left or right white line is not recognized. There may be a case in which driver assistance can be performed to some degree even if one of the left and right white lines is recognized, which is required to comply with a safety requirement depending on countries (NCAP (New Car Assessments Program) in USA). Thus, even if one of the left and right white lines is not recognized, it is preferred that the display device displays the white line icon to notify the driver.
FIG. 1B illustrates an example of a display status of the white line if only the right white line is recognized, and FIG. 1C illustrates an example of a display status of the white line if only the left white line is recognized. As illustrated in FIGS. 1B and 1C, the LDW/LKA can notify the driver of the white line recognition status by displaying the recognized white line in a bold manner and the unrecognized white line in a outline manner.
However, as illustrated in FIGS. 1B and 1C, there is a problem that displaying only the recognized one of the white lines in a bold manner leads to a deviation with respect to the recognition by the driver. Specifically, when the vehicle travels in the lane such that the vehicle is biased to the right or left white line, one of the white lines (the white line opposite to the closer white line) goes out of a white line recognition area due to a limit of the angle of view of the camera or the white line recognition area (i.e., an image processing area) and thus one of the white lines, which goes out of the white line recognition area, becomes unrecognized. However, even in this case, since the right and left white lines are in the view of the driver, there may be a case where the driver wonders why one of the white lines is not recognized.
FIG. 2A is a diagram for illustrating an example of the angle of view of the camera. As illustrated in FIG. 2A, for the purpose of the image processing such as the white line recognition, the LDW/LKA uses only the white lines in a predetermined area in front of the vehicle and within the angle of view. The farther end of the area is few tens meters away from the vehicle so that the accuracy of the white line recognition can be maintained, while the nearer end of the area is about ten meters from the vehicle which is within the angle of view and not shielded by a hood or the like. If the angle of view can be enlarged, the LDW/LKA can recognize the white line from the nearer distance, thereby preventing a situation in which only the farther white line is not recognized when the vehicle becomes closer to one of the white lines.
However, even if the angle of view is enlarged, the number of the pixels doesn't change in the camera as a whole. Therefore, the number of the pixels of the white lines is reduced when the angle of view is enlarged and thus the image processing accuracy for the farther scene is reduced. In this case, accuracy in calculating curve radius or a curvature of the lane, in particular, is reduced.
Further, the camera of the LDW/LKA is often shared with other driver assist apparatuses which require the image processing for the farther scene. For example, an automatic high beam apparatus, which automatically switches a beam pattern of front headlamps between a high beam pattern and a low beam pattern, uses the camera to detect a preceding vehicle and an oncoming vehicle at a few hundreds of meters ahead of the vehicle and switch the beam pattern. For this reason, it is not desirable to reduce the detection accuracy of the preceding vehicle and the oncoming vehicle by enlarging the angle of view. Further, for a pedestrian detecting apparatus which calls attention to the driver when it detects a pedestrian, if the pedestrian at the farther distance cannot be detected, the output of the call for attention may be delayed. Thus, it is not desirable to reduce the detection accuracy of the pedestrian by enlarging the angle of view. For such reasons, the camera (lens) with a relatively narrow angle of view is adopted in the LDW/LKA not to reduce the image processing accuracy for the farther scene.
FIG. 2B is a diagram for illustrating an example of a limitation on white line recognition areas. In general, a calculation load for the image processing such as the white line recognition is relatively high. On the other hand, areas in which the white lines exist are a right side and a left side of the image rather than a center. Thus, in order to reduce the processing load, the LDW/LKA recognizes the white lines only from a minimum necessary predetermined area (left and right white line recognition areas). In this way, since there is such a limitation on the white line recognition area, there may be a case where the white line does not exist in the left or right white line recognition area if the vehicle travels in the lane such that the vehicle is biased to the right or left white line.
FIGS. 3A and 3B are diagrams for illustrating a situation in which the left white line is out of the left white line recognition area. As illustrated in FIG. 3A, when the vehicle becomes closer to the right white line, the left white line becomes out of the left white line recognition area as illustrated in FIG. 3B. Thus, according to prior art, when the vehicle becomes closer to the right white line, such a white line icon as illustrated in FIGS. 1B and 1C are merely displayed, which leads to strange feelings of the driver.
[Patent Document 1] Japanese Laid-open Patent Publication No. 2007-125968